348 research outputs found

    Review of Computational approaches for predicting the physicochemical and biological properties of nanoparticles

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    In the growing field of nanotechnology there is a need to determine the physicochemical and potential toxicological properties of nanomaterials since many industrial, medical and consumer applications are based on an understanding of these properties and on a controlled exposure to the materials. This document provides a literature review on the current status of computational studies aimed at predicting the physicochemical properties and biological effects (including toxicity) of nanomaterials, with an emphasis on medical applications. Although a number of models have been published for physicochemical property prediction, very few models have been published for predicting biological effects, toxicity or the underlying mechanisms of action. This is due to two main reasons: a) nanomaterials form a colloidal phase when in contact with biological systems making the definition and calculation of properties (descriptors) suitable for the prediction of toxicity a new and challenging task, and b) nanomaterials form a very heterogeneous class of materials, not only in terms of their chemical composition, but also in terms of size, shape, agglomeration state, and surface reactivity. There is thus an urgent need to extend the traditional structure-activity paradigm to develop methods for predicting the toxicity of nanomaterials, and to make the resulting models readily available. This document concludes by proposing some lines of research to fill the gap in knowledge and predictive methodologyJRC.I.6-Systems toxicolog

    Enhanced aqueous solubility and photodimerization of polycyclic aromatics mediated by γ-Cyclodextrin derivatives

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    A series of hydrophilic γ-cyclodextrin (CD) thioethers were synthesized and selected as hosts. They were able to solubilize polycyclic aromatic guests in water to much higher extents than native CDs. The results of experimental (phase-solubility method and fluorescence spectroscopy) and theoretical (quantum mechanical and space-filling calculations) investigations confirmed the formation of 1:2 CD-guest complexes in aqueous solution. True molecular solutions of C60 were obtained by dissolving C60 in aqueous solutions of γ-CD thioethers and confirmed by using dynamic light scattering method. We also succeed to obtain stable aqueous dispersions of C60, by employing the methods based on solvent exchange in presence of γ-CD thioethers. γ-CD thioether acted as a supramolecular catalytic nano-reaction vessel and facilitates the photodimerization of the aromatic guests in aqueous medium. High quantum yields of the photodimerizations in presence of γ-CD thioethers were obtained when compared to those of the aromatic guests in host-free solutions. The orientation of two molecules of acenaphthylene when bound to CD led to the selective formation of the trans product upon irradiation in quantitative yield for the first time. Excitation of the 1:2 CD–guest inclusion complex of coumarin in water resulted in an increased yield of syn head-to-head dimer. Other photoproducts of coumarin which typically produced in the absence of the template were remarkably suppressed by salting out effect.Eine Reihe von hydrophilen γ-Cyclodextrin (CD) Thioethern wurden in der vorliegenden Dissertation synthetisiert. Im Vergleiche zu nativen CDs konnten sie polyzyklische aromatische Gäste in Wasser besser solubilisieren. Durch experimentelle und theoretische Untersuchungen wurde die Bildung von 1:2 CD–Gast Komplexen in wässriger Lösung bestätigt. Durch Verwendung von γ-CD Thioethern wurden wässrige Lösungen von C60 erhalten. Dies wurde mittels Dynamischer Lichtstreuung belegt. Mit Methoden auf der Grundlage des Lösungsmittelsaustausches haben wir in gegenwart von γ-CD Thioethern beständige wässrige Dispersionen mit C60 erfolgreich hergestellt. γ-CD Thioether werden als supramolekulare katalytische Nano-Reaktionsgefäße angesehen und ermöglichen die Photodimerisierung von aromatischen Gästen im wässrigem Medium. Hohe Quantenausbeuten wurden bei der Photodimerisierung von aromatischen Gästen in gegenwart von γ-CD Thioethern erhalten, im Vergleich zu Gast freien Lösungen. Durch Bestrahlung wurde aufgrund der Orientierung von Acenaphthylen im CD zum ersten Mal selektiv in quantitativer Ausbeute das trans Produkt erhalten. Durch Anregung von 1:2 CD–Cumarin Wirts–Gast–Verbindungen in Wasser wurde eine höhere Ausbeute von syn head-to-head Dimeren erreicht. Weitere Photoprodukte von Cumarin die typischerweise in Abwesenheit von Templaten entstehen konnten bemerkenswerterweise durch Aussalzeffekte unterdrückt werden

    Flexible decapyrrylcorannulene hosts

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    球形笼状的富勒烯是上个世纪末最重要的科学发现之一,但对富勒烯的精确几何结构的认识却困难重重,原因是单晶中球形分子的取向往往是无序的,需通过笼外衍生或通过八乙基金属卟啉-富勒烯超分子主客体组装来固定富勒烯的取向,然后利用常用的单晶衍射分析技术来精确表征富勒烯的几何结构。然而许多富勒烯新结构因无法与卟啉主体形成高质量的单晶至今仍无法利用X射线衍射技术进行结构分析,直接制约了对富勒烯形成机理及结构-性能关系的深入认识。功能团簇材料创新研究群体的谢素原、张前炎课题组另辟蹊径地从曲面结构的十氯碗烯C20Cl10出发,合成了十吡咯取代的碗烯分子C20(C4H4N)10。结构分析表明该分子的结构特征是碗烯的碳框架与十个吡咯基团通过单键相连。实验还证明,用甲基去取代吡咯3, 4-位置的氢并不利于富勒烯与碗烯衍生物形成有序的超分子组装体,理论研究进一步诠释了十个吡咯‘手指’的集体贡献比单个碗烯‘手掌’更大的原因。该研究工作是功能团簇材料创新研究群体长期积累,并由校内外十多位研究人员共同努力完成。徐云彦(2014级硕士生)、田寒蕊(2014级博士生)和李姝慧(2016年进站博士后)为该论文共同第一作者。【Abstract】The assembly of spherical fullerenes, or buckyballs, into single crystals for crystallographic identification often suffers from disordered arrangement. Here we show a chiral configuration of decapyrrylcorannulene that has a concave ‘palm’ of corannulene and ten flexible electron-rich pyrryl group ‘fingers’ to mimic the smart molecular ‘hands’ for self-adaptably cradling various buckyballs in a (+)hand-ball-hand(−) mode. As exemplified by crystallographic identification of 15 buckyball structures representing pristine, exohedral, endohedral, dimeric and hetero-derivatization, the pyrryl groups twist with varying dihedral angles to adjust the interaction between decapyrrylcorannulene and fullerene. The self-adaptable electron-rich pyrryl groups, susceptible to methylation, are theoretically revealed to contribute more than the bowl-shaped palm of the corannulene in holding buckyball structures. The generality of the present decapyrrylcorannulene host with flexible pyrryl groups facilitates the visualization of numerous unknown/unsolved fullerenes by crystallography and the assembly of the otherwise close-packed spherical fullerenes into two-dimensional layered structures by intercalation.This research was supported by the National Natural Science Foundation of China (21771152, 21721001, 21827801, 51572231, 51572254, 21571151, 2170010228), the 973 Program of China (2014CB845601 and 2015CB932301), the China Postdoctoral Science Foundation (2016M602067), the National Key Research and Development Program of China (2017YFA0402800), and the Fundamental Research Funds for the Central Uni- versities (20720170028, 20720160084). Q.Y.Z. is particularly grateful to 21771152, 2015CB932301, 20720170028, 20720160084; S.F.Y. is particularly grateful to 51572254 and 2017YFA0402800; S.Y.X. is particularly grateful to 21721001 and 51572231; L.S.Z. is particularly grateful to 21827801; S.L.D. is particularly grateful to 21571151; S.H.L. is particularly grateful to 2170010228 and 2016M602067. 研究工作得到国家自然科学基金(21771152、21721001、21827801、51572231、51572254, 21571151、2170010228)、科技部973计划(2014CB845601、2015CB932301)和重点研发计划(2017YFA0402800)、国家博士后科学基金、中央高校基本科研业务费等的资助

    Improved model for fullerene C 60 solubility in organic solvents based on quantum-chemical and topological descriptors

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    Abstract Fullerenes are sparingly soluble in many solvents. The dependence of fullerene's solubility on molecular structure of the solvent must be understood in order to manage efficiently this class of compounds. To find such dependency ab initio quantum-chemical calculations in combination with quantitative structure-property relationship (QSPR) tool were used to model the solubility of fullerene C 60 in 122 organic solvents. A genetic algorithm and multiple regression analysis (GA-MLRA) were applied to generate correlation models. The best performance is accomplished by the four-variable MLRA model with prediction coefficient r test 2 = 0.903. This study reveals a correlation of highest occupied molecular orbital energy (HOMO), certain heteroatom fragments, and geometrical parameters with solubility. Several other important parameters of solvents that affect the C 60 solubility have been also evaluated by the QSPR analysis. The employed GA-MLRA approach enhanced by application of quantum-chemical calculations yields reliable results, allowing one to build simple, interpretable models that can be used for predictions of C 60 solubility in various organic solvents

    Modular Synthesis of Amphiphilic Networks with Guest-host Capabilities

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    Herein is described a controlled modular method for nanoscopic polymer network synthesis. Nodal points, such as cyclodextrins, are well defined, as are the cross-linking tie chains (e.g. polyethylene oxide), which are of known molecular weight, and lead to species with guest-host complexation abilities. Tie chains are varied by length and nature, that is, nonpolar or polar, resulting in hydrophobic or amphiphilic networks, respectively. Methods of functionalization can result in the stoichiometric control of network densities, and nodal points, chain orientation and chemistry can be regulated. When formed into films, these networks can sequester small molecules, such as C60 fullerene, through guest-host interactions. Interrogation of mono-functionalized and polymerized products was undertaken by solid state nuclear magnetic resonance experiments. Networked materials, though insoluble in common solvents, swell to varying degrees in nonpolar, polar protic, polar aprotic and halogenated solvents. Simple modular assembly methods for synthesizing amphiphilic polymer networks with specific linker lengths between cross-link sites, tailored hydrophilicity versus hydrophobicity, and active nodes are detailed.Chemistr

    QUANTITATIVE ANALYSIS AND STRUCTURAL CHARACTERIZATION OF CARBONACEOUS PITCHES

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    Both petroleum pitches and pitches derived from pure polycyclic aromatic hydrocarbons (PAHs) are oligomeric materials that can serve as precursors for a wide variety of advanced carbon materials. The goal of this study was the structural characterization and quantitative analysis of the dominant constituent oligomers and species present in these pitches. A key requirement for such work is the ability to fractionate these complex mixtures into samples of narrow molecular weight distribution (mol wt; MWD) that can be used as standards. To this end, semicontinuous (or semibatch) dense-gas/supercritical extraction (DGE/SCE) was used to produce monomer, dimer, and trimer fractions of selected pitches (i.e., M-50 and pyrene pitch) during the course of this work. Matrix-assisted, laser desorption/ionization mass spectrometry (MALDI-MS) was then used to develop a reliable quantitative analysis method for these polydisperse mixtures of petroleum macromolecules. The interrelationships among MALDI sample preparation methods, analyte MWD, and MALDI response for well-defined, oligomeric pitch systems were investigated in order to identify a reliable sample preparation method. Based on the findings, solvent-free (vs. solvent-based) sample preparation was selected for the quantitative analysis study. DGE-derived, oligomeric cuts were used as standards, and the method of standard addition was successfully applied for the first time to the quantitative MALDI analysis of a polydisperse system using a solvent-free sample preparation method. Advanced separation and analytical characterization techniques were used to determine the molecular structures of the constituent species present in the monomer and dimer fractions of a thermally polymerized petroleum pitch, and of a catalytically polymerized pyrene pitch. Even though the starting material for the pyrene polymerization was pure pyrene, alkylated species were found to be present, albeit at low concentrations. Alkylpyrene isomers and the pyrene dimer isomer were isolated by DGE followed by HPLC and then unambiguously identified via MALDI and UV-vis. Dimer species were found to consist exclusively of monomer units connected by 6-membered rings. This is in dramatic contrast to our experience with both anthracene and petroleum pitches formed via thermal polymerization, where 5-membered connecting rings are the predominant method of polymerization

    Perfluoroalkylfullerenes

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    New chemical derivatives that possess the greatest variety of addition patterns than any other class of fullerene derivatives represent an important addition to the existing classes of perfluorocarbons, that is, compounds that are composed only of the two types of atoms, carbon and fluorine. These include aromatic and aliphatic perfluorocarbons such as perfluorodecalin, perfluorononane, hexafluorobenzene, etc., which are important as fluorous solvents used in medicine. The propensity of perfluoroalkylfullerenes (PFAFs) to readily crystallize from organic solutions upon slow evaporation in open air provided a straightforward access to their molecular structures via X-ray crystallography. Another crucial aspect that ensures future success in the characterization of numerous PFAFs of higher fullerenes and endohedral metallofullerenes is the possibility to apply HPLC methodologies to the separation of product mixtures. PFAFs, especially those of C60 and C70, are unique fullerene derivatives in terms of the number of structurally characterized derivatives with different number of RF groups and different addition patterns

    Application of Molecular Modeling in the Noncovalent Dispersion of Carbon Nanomaterials

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    Molecular modeling is a powerful tool to better understand the intermolecular interactions of carbon nanostructures. It provides structures and energies not easily obtainable from experiments and predicts properties that can be tested experimentally. Intermolecular interactions play an important role in the aggregation of various carbon nanomaterials. Three molecular modeling studies of carbon nanomaterial dispersions are presented in this dissertation, with an emphasis on illustrating how effective these theoretical techniques are in providing insight on the selection of dispersion additives. To achieve our goals, we employed molecular mechanics based methods, along with semi-empirical methods, and quantum mechanical methods, such as density functional theory. Of these techniques, molecular mechanics based methods were the more frequently applied. Chapter I serves as a brief review of computational methods with an emphasis on molecular mechanics. The first project (Chapter II) includes theoretical studies on the dispersion of single-walled carbon nanotubes (SWNTs) via non-covalent attachment of dispersing polymers. This effort involved the investigation of the binding affinities between specific polymers and SWNTs. Dispersion of SWNTs has been of great interest for many years due to numerous applications promised by their unique combination of electronic, mechanical, chemical, and thermal properties. SWNTs are incompatible with most solvents and polymers, which results in poor dispersion of these compounds in the polymer matrix. Van der Waals attraction among tubes over a large surface area leads to significant agglomeration, thus preventing efficient transfer of their superior properties to the matrix. Improving our fundamental understanding of the interactions of polymer- SWNT interactions at the molecular level is needed for the development of new materials based on SWNTs. Structures of SWNT-polymer complexes were optimized using molecular mechanics, employing COMPASS forcefield. The optimized complexes enabled a morphological analysis of the arrangement of polymer strands on the SWNT surface and calculations of the intermolecular interaction energies. Our calculations identified a strong binding affinity between SWNTs and conjugated polymers containing heteroatoms. The inclusion of solvent effects in the theoretical calculations produced results matching experimental observations from laboratory dispersion studies. The second project (Chapter III) consists of computational studies on the potential dispersion of metallic nitride fullerenes (MNFs), e.g. Sc3N@Cgo, using a solventcompatible complexing agent. MNFs have a unique hollow-ball shape built from 12 carbon pentagons and 30 hexagons, possessing truncated icosahedra symmetry and encapsulating a trimetallic-nitride cluster at the core of the cage. This unique structure results in its distinctive physical and chemical properties. The ability of MNFs to bring a functional metal to polymeric nano-composite systems opens up the possibility for extraordinary properties, e.g. magnetic, electroactive, and radioactive properties, which hold great promise for medical, optical, and electronic applications. Incorporation of MNF materials in a polymer support material involves the uniform dispersion of MNFs in the matrix. Due to the all-carbon cage, MNFs are very hydrophobic materials and possess minimal solubility in common organic solvents (mg/mL scale), monomers, and polymers, complicating the dispersion process. The ability to disperse MNFs in polymers is paramount to realizing the potential of these materials in future commercial applications. MNFs are difficult to chemically functionalize without altering the desirable intrinsic properties; therefore, an important aspect of this work is the focus on potential non-covalent dispersion techniques using co-additives, which is a versatile, nondamaging chemistry and preserves all of the intrinsic properties of MNF. Here we studied the interactions between dispersing additive molecules and MNFs using molecular mechanics and specifically calculating interaction energies between MNFs and a variety of additive molecules. A series of resorcinarene and calixarene compounds were surveyed, and characteristics of suitable candidates were identified. Select resorcinarene and calixarene compounds were used in experimental MNF dispersion studies, analyzing samples by particle size measurements and NMR chemical shifts. These experimental studies supported theoretical results, and the dispersion of MNFs in DMF was achieved. In a third project (Chapter IV), interactions of naphthenic acids with crude oil asphaltenes were examined; thereby contributing significantly to the volume of knowledge available describing the affinities of these acidic and basic components of crude oil. In this project a molecular mechanical analysis with an accepted structure of asphaltene was performed, and intermolecular interactions between asphaltene and naphthenic acids dispersants were calculated. The geometries of the asphaltene - naphthenic acid complexes were optimized and five resultant regioisomers of the asphaltene-naphthenic acid complex were analyzed. The molecular mechanical calculations suggest that the intermolecular interactions between asphaltene and naphthenic acids consist of vdW and electrostatic interactions
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